Papillomavirus truncated L1 protein and fusion protein constructs

ABSTRACT

Vaccine formulations comprising viral capsomeres are disclosed along with methods for their production. Therapeutic and prophylactic methods of use for the vaccine formulations are also disclosed.

This is a Divisional Application of U.S. patent application Ser. No. 09/824,017, filed Apr. 3, 2001, now U.S. Pat. No. 6,649,167, which is in turn a Continuation Application of U.S. patent application Ser. No. 09/026,896, filed Feb. 20, 1998, now abandoned.

FIELD OF THE INVENTION

The present invention relates to vaccine formulations comprising papilloma virus proteins, either as fusion proteins, truncated proteins, or truncated fusion proteins. The invention further embraces methods for producing capsomeres of the formulations, as well as prophylactic and therapeutic methods for their use.

BACKGROUND

Infections with certain high-risk strains of genital papilloma viruses in humans (HPV)—for example. HPV 16, 18, or 45—are believed to be the main risk factor for the formation of malignant tumors of the anogenital tract. Of the possible malignancies, cervical carcinoma is by far the most frequent: according to an estimate by the World Health Organization (WHO), almost 500,000 new cases of the disease occur annually. Because of the frequency with which this pathology occurs, the connection between HPV infection and cervical carcinoma has been extensively examined, leading to numerous generalizations.

For example, precursor lesions of cervical intraepithelial neoplasia (CIN) are known to be caused by papilloma virus infections [Crum, New Eng. J. Med. 310:880–883 (1984)]. DNA from the genomes of certain HPV types, including for example, strains 16, 18, 33, 35, and 45, have been detected in more than 95% of tumor biopsies from patients with this disorder, as well as in primary cell lines cultured from the tumors. Approximately 50 to 70% of the biopsied CIN tumor cells have been found to include DNA derived only from HPV 16.

The protein products of the HPV 16 and HPV 18 early genes E6 and E7 have been detected in cervical carcinoma cell lines as well as in human keratinocytes transformed in vitro [Wettstein, et al., in PAPILLOMA VIRUSES AND HUMAN CANCER, Pfister (Ed.),CRC Press: Boca Raton, Fla. 1990 pp 155–179] and a significant percentage of patients with cervical carcinoma have anti-E6 or anti-E7 antibodies. The E6 and E7 proteins have been shown to participate in induction of cellular DNA synthesis in human cells, transformation of human keratinocytes and other cell types, and tumor formation in transgenic mice [Arbelt, et al., J. Virol., 68:4358–4364 (1994): Auewarakul, et al., Mol. Cell. Biol. 14:8250–8258 (1994); Barbosa, et al., J. Virol. 65:292–298 (1991); Kaur, et al., J. Gen. Virol. 70:1261–1266 (1989): Schlegel, et al., EMBO J., 7:3181–3187 (1988)]. The constitutive expression of the E6/E7 proteins appears to be necessary to maintain the transformed condition of HPV-positive tumors.

Despite the capacity of some HPV strains to induce neoplastic phenotypes in vivo and in vitro, still other HPV types cause benign genital warts such as condylomata acuminata and are only rarely associated with malignant tumors [Ikenberg. In Gross, et al., (eds.) GENITAL PAPILLOMAVIRUS INFECTIONS. Springer Verlag: Berlin, pp., 87–112]. Low risk strains of this type include, for example, HPV 6 and 11.

Most often, genital papilloma viruses are transmitted between humans during intercourse which in many instances leads to persistent infection in the anogenital mucous membrane. While this observation suggests that either the primary infection induces an inadequate immune response or that the virus has developed the ability to avoid immune surveillance, other observations suggest that the immune system is active during primary manifestation as well as during malignant progression of papilloma virus infections [Altmann et al. in VIRUSES AND CANCER, Minson et al., (eds.) Cambridge University Press, (1994) pp. 71–80].

For example, the clinical manifestation of primary infection by rabbit and bovine papilloma virus can be prevented by vaccination with wart extracts or viral structural proteins [Altmann, et al., supra; Campo, Curr. Top. In Microbiol and Immunol. 186:255–266 (1994); Yindle and Frazer, Curr. Top. In Microbiol. and Immunol. 186;217–253 (1994)]. Rodents previously vaccinated with vaccinia recombinants encoding HPV 16 early proteins E6 or E7, or with synthetic E6 or E7 peptides, are similarly protected from tumor formation after inoculation of HPV 16 transformed autologous cells [Altman, et al., supra; Campo, et al., supra; Yindle and Frazer, et al. supra]. Regression of warts can be induced by the transfer of lymphocytes from regressor animals following infection by animal papilloma viruses. Finally, in immunosuppressed patients, such as, for example, recipients of organ transplants or individuals infected with HIV, the incidence of genital warts. CIN, and anogenital cancer is elevated.

To date, no HPV vaccinations have been described which comprise human papilloma virus late L1 protein in the form of capsomeres which are suitable both for prophylactic and therapeutic purposes. Since the L1 protein is not present in malignant genital lesions, vaccination with L1 protein does not have any therapeutic potential for these patients. Construction of chimeric proteins, comprising amino acid residues from L1 protein and, for example E6 or E7 protein, which give rise to chimeric capsomeres, combines prophylactic and therapeutic functions of a vaccine. A method for high level production of chimeric capsomeres would therefore be particularly desirable, in view of the possible advantages offered by such a vaccine for prophylactic and therapeutic intervention.

Thus there exists a need in the art to provide vaccine formulations which can prevent or treat HPV infection. Methods to produce vaccine formulations which overcome problems known in the art to be associated with recombinant HPV protein expression and purification would manifestly be useful to treat the population of individuals already infected with HPV as well as useful to immunize the population of individuals susceptible to HPV infection.

SUMMARY OF THE INVENTION

The present invention provides therapeutic and prophylactic vaccine formulations comprising chimeric human papilloma capsomeres. The invention also provides therapeutic methods for treating patients infected with an HPV as well as prophylactic methods for preventing HPV infection in a susceptible individual. Methods for production and purification of capsomeres and proteins of the invention are also contemplated.

In one aspect of the invention, prophylactic vaccinations for prevention of HPV infection are considered which incorporate the structural proteins L1 and L2 of the papilloma virus. Development of a vaccine of this type faces significant obstacles because papilloma viruses cannot be propagated to adequate titers in cell cultures or other experimental systems to provide the viral proteins in sufficient quantity for economical vaccine production. Moreover, recombinant methodologies to express the proteins are not always straightforward and often results in low protein yield. Recently, virus-like particles (VLPs), similar in make up to viral capsid structures, have been described which are formed in Sf-9 insect cells upon expression of the viral proteins L1 and L2 (or L1 on its own) using recombinant vaccinia or baculovirus. Purification of the VLPs can be achieved very simply by means of centrifugation in CsCl or sucrose gradients [Kimbauer, et al. Proc. Natl. Acad. Sci. (USA), 99:12180–12814 (1992): Kirnbaurer, et al. J. Virol. 67:6929–6936 (1994); Proso, et al., J. Virol. 6714:1936–1944 (1992): Sasagawa, et al., Virology 2016:126–195 (1995); Volpers, et al. J. Virol. 69:3258–3264 (1995); Zhou, et al., J. Gen. Virol. 74:762–769 (1993): Zhou, et al., Virology 185:251–257 (1991)]. WO 93/02184 describes a method in which papilloma virus-like particles (VLPs) are used for diagnostic applications or as a vaccine against infections caused by the papilloma virus. WO 94/00152 describes recombinant production of L1 protein which mimics the conformational neutralizing epitope on human and animal papilloma virions.

In another aspect of the invention, therapeutic vaccinations are provided to relieve complications of, for example, cervical carcinoma or precursor lesions resulting from papilloma virus infection, and thus represent an alternative to prophylactic intervention. Vaccinations of this type may comprise early papilloma virus proteins, principally E6 or E7, which are expressed in the persistently infected cells. It is assumed that, following administration of a vaccination of this type, cytotoxic T-cells might be activated against persistently infected cells in genital lesions. The target population for therapeutic intervention is patients with HPV-associated pre-malignant or malignant genital lesions. PCT patent application WO 93/20844 discloses that the early protein E7 and antigenic fragments thereof of the papilloma virus from HPV or BPV is therapeutically effective in the regression, but not in the prevention, of papilloma virus tumors in mammals. While early HPV proteins have been produced by recombinant expression in E. coli or suitable eukaryotic cell types, purification of the recombinant proteins has proven difficult due to inherent low solubility and complex purification procedures which generally require a combination of steps, including ion exchange chromatography, gel filtration and affinity chromatography.

According to the present invention, vaccine formulations comprising papilloma virus capsomeres are provided which comprise either: (i) a first protein that is an intact viral protein expressed as a fusion protein comprised in part of amino acid residues from a second protein; (ii) a truncated viral protein: (iii) a truncated viral protein expressed as a fusion protein comprised in part of amino acid residues from a second protein, or (iv) some combination of the three types of proteins. According to the invention, vaccine formulations are provided comprising capsomeres of bovine papilloma virus (BPV) and human papilloma virus. Preferred bovine virus capsomeres comprise protein from bovine papilloma virus type I. Preferred human virus capsomeres comprise proteins from any one of human papilloma virus strains HPV6, HPV11, HPV16, HPV18, HPV33, HPV35, and HPV45. The most preferred vaccine formulations comprise capsomeres comprising proteins from HPV16.

In one aspect, capsomere vaccine formulations of the invention comprise a first intact viral protein expressed as a fusion protein with additional amino acid residues from a second protein. Preferred intact viral proteins are the structural papilloma vial proteins L1 and L2. Capsomeres comprised of intact viral protein fusions may be produced using the L1 and L2 proteins together or the L1 protein alone. Preferred capsomeres are made up entirely of L1 fusion proteins, the amino acid sequence of which is set out in SEQ ID NO: 2 and encoded by the polynucleotide sequence of SEQ ID NO: 1. Amino acids of the second protein can be derived from numerous sources (including amino acid residues from the first protein) as long as the addition of the second protein amino acid residues to the first protein permits formation of capsomeres. Preferably, addition of the second protein amino acid residues inhibits the ability of the intact viral protein to form virus-like particle structures; most preferably, the second protein amino acid residues promote capsomere formation. In one embodiment of the invention, the second protein may be any human tumor antigen, viral antigen, or bacterial antigen which is important in stimulating an immune response in neoplastic or infectious disease states. In a preferred embodiment, the second protein is also a papilloma virus protein. It also preferred that the second protein be the expression product of papilloma virus early gene. It is also preferred, however, that the second protein be selected from group of E1, E2, E3, E4, E5, E6, and E7—early gene products encoded in the genome of papilloma virus strains HVP6, HPV11, HPV18, HPV33, HPV35, or HPV 45. It is most preferred that the second protein be encoded by the HPV16 E7 gene, the open reading frame of which is set out in SEQ ID NO: 3. Capsomeres assembled from fusion protein subunits are referred to herein as chimeric capsomeres. In one embodiment, the vaccine formulation of the invention is comprised of chimeric capsomeres wherein L1 protein amino acid residues make up approximately 50 to 99% of the total fusion protein amino acid residues. In another embodiment, L1 amino acid residues make up approximately 60 to 90% of the total fusion protein amino acid residues; in a particularly preferred embodiment, L1 amino acids comprise approximately 80% of the fusion protein amino acid residues.

In another aspect of the invention, capsomere vaccine formulations are provided that are comprised of truncated viral proteins having a deletion of one or more amino acid residues necessary for formation of a virus-like particle. It is preferred that the amino acid deletion not inhibit formation of capsomeres by the truncated protein, and it is most preferred that the deletion favor capsomere formation. Preferred vaccine formulations of this type include capsomeres comprised of truncated L1 with or without L2 viral proteins. Particularly preferred capsomeres are comprised of truncated L1 proteins. Truncated proteins contemplated by the invention include those having one or more amino acid residues deleted from the carboxy terminus of the protein, or one or more amino acid residues deleted from the amino terminus of the protein, or one or more amino acid residues deleted from an internal region (i.e., not from either terminus) of the protein. Preferred capsomere vaccine formulations are comprised of proteins truncated at the carboxy terminus. In formulations including L1 protein derived from HPV16, it is preferred that from 1 to 34 carboxy terminal amino acid residues are deleted. Relatively shorter deletions are also contemplated which offer the advantage of minor modification of the antigenic properties of the L1 proteins and the capsomeres formed thereof. It is most preferred, however, that 34 amino acid residues be deleted from the L1 sequence, corresponding to amino acids 472 to 505 in HPV16 set out in SEQ ID NO: 2, and encoded by the polynucleotide sequence corresponding to nucleotides 1414 to 1516 in the human HPV16 L1 coding sequence set out in SEQ ID NO: 1.

When a capsomere vaccine formulation is made up of proteins bearing an internal deletion, it is preferred that the deleted amino acid sequence comprise the nuclear localization region of the protein. In the L1 protein of HPV 16, the nuclear localization signal is found from about amino acid residue 499 to about amino acid residue 505. Following, expression of L1 proteins wherein the NLS has been deleted, assembly of capsomere structures occurs in the cytoplasm of the host cell. Consequently, purification of the capsomeres is possible from the cytoplasm instead of from the nucleus where intact L1 proteins assemble into capsomeres. Capsomeres which result from assembly of truncated proteins wherein additional amino acid sequences do not replace the deleted protein sequences are necessarily not chimeric in nature.

In still another aspect of the invention, capsomere vaccine formulations are provided comprising truncated viral protein expressed as a fusion protein adjacent amino acid residues from a second protein. Preferred truncated viral proteins of the invention are the structural papilloma viral proteins L1 and L2. Capsomeres comprised of truncated viral protein fusions may be produced using L1 and L2 protein components together or L1 protein alone. Preferred capsomeres are those comprised of L1 protein amino acid residues. Truncated viral protein components of the fusion proteins include those having one or more amino acid residues deleted from the carboxy terminus of the protein, or one or more amino acid residues deleted from the amino terminus of the protein, or one or more amino acid residues deleted from an internal region (i.e., not from either terminus) of the protein. Preferred capsomere vaccine formulations are comprised of proteins truncated at the carboxy terminus. In those formulations including, L1 protein derived from HPV16, it is prefer that from 1 to 34 carboxy terminal amino acid residues are deleted. Relatively shorter deletions are also contemplated that offer the advantage of minor modification of the antigenic properties of the L1 protein component of the fusion protein and the capsomeres formed thereof. It is most preferred, however, that 34 amino acid residues be deleted from the L1 sequence, corresponding to amino acids 472 to 505 in HPV16 set out in SEQ ID NO: 2, and encoded by the polynucleotide sequence corresponding to nucleotides 1414 to 1516 in the human HPV16 L1 coding sequence set out in SEQ ID NO: 1. When the vaccine formulation is comprised of capsomeres made up of proteins bearing an internal deletion, it is preferred that the deleted amino acid sequence comprise the nuclear localization region, or sequence, of the protein.

Amino acids of the second protein can be derived from numerous sources as long as the addition of the second protein amino acid residues to the first protein permits formation of capsomeres. Preferably, addition of the second protein amino acid residues promotes or favors capsomere formation. Amino acid residues of the second protein can be derived from numerous sources, including amino acid residues from the first protein. In a preferred embodiment, the second protein is also a papilloma virus protein. It also preferred that the second protein be the expression product of papilloma virus early gene. It is most preferred, however, that the second protein be selected from group of early gene products encoding by papilloma virus E1, E2, E3, E4, E5, E6, and E7 genes. In one embodiment, the vaccine formulation of the invention is comprised of chimeric capsomeres wherein L1 protein amino acid residues make up approximately 50 to 99% of the total fusion protein amino acid residues. In another embodiment, L1 amino acid residues make up approximately 60 to 90% of the total fusion protein amino acid residues; in a particularly preferred embodiment, L1 amino acids comprise approximately 80% of the fusion protein amino acid residues.

In a preferred embodiment of the invention, proteins of the vaccine formulations are produced by recombinant methodologies, but in formulations comprising intact viral protein, the proteins may be isolated from natural sources. Intact proteins isolated from natural sources may be modified in vitro to include additional amino acid residues to provide a fusion protein of the invention using covalent modification techniques well known and routinely practiced in the art. Similarly, in formulations comprising truncated viral proteins, the proteins may be isolated from natural sources as intact proteins and hydrolyzed in vitro using chemical hydrolysis or enzymatic digestion with any of a number of site-specific or general proteases, the truncated protein subsequently modified to include additional amino acid resides as described above to provide a truncated fusion protein of the invention.

In producing capsomeres, recombinant molecular biology techniques can be utilized to produce DNA encoding either the desired intact protein, the truncated protein, or the truncated fusion protein. Recombinant methodologies required to produce a DNA encoding a desired protein are well known and routinely practiced in the art. Laboratory manuals, for example Sambrook, et al. (eds.), MOLECULAR CLONING: A LABORATORY MANUAL. Cold Spring Harbor Press: Cold Spring Harbor, N.Y. (1989) and Ausebel et al. (eds.). PROTOCOLS IN MOLECULAR BIOLOGY. John Wiley & Sons. Inc. (1994–1997), describe in detail techniques necessary to carry out the required DNA manipulations. For large-scale production of chimeric capsomeres, protein expression can be carried out using either viral or eukaryotic vectors. Preferable vectors include any of the well known prokaryotic expression vectors, recombinant baculoviruses, COS cell specific vectors, vaccinia recombinants, or yeast-specific expression constructs. When recombinant proteins are used to provide capsomeres of the invention, the proteins may first be isolated from the host cell of its expression and there-r incubated under conditions which permit self-assembly to provide capsomeres. Alternatively, the proteins may be expressed under conditions wherein capsomeres are formed in the host cell.

The invention also contemplates processes for producing capsomeres of the vaccine formulations. In one method, L1 proteins are expressed from DNA encoding six additional histidines at the carboxy terminus of the L1 protein coding sequence. L1 proteins expressed with additional histidines (His L1 proteins) are most preferably expressed in E. coli and the His L1 proteins can be purified using nickel affinity chromatography. His L1 proteins in cell lysate are suspended in a denaturation buffer, for example. 6 M guanidine hydrochloride or a buffer of equivalent denaturing capacity, and then subjected to nickel chromatography. Protein eluted from the nickel chromatography step is renatured, for example in 150 mM NaCl. 1 mM CaCl₂. 0.01% Triton-X 100, 10 mM HEPES (N-2-hydroxyethyl piperazine-N′-2 ethane sulfonic acid), pH 7.4. According to a preferred method of the invention, assembly of capsomeres takes place after dialysis of the purified proteins, preferably after dialysis against 150 mM NaCl. 25 mM Ca²⁺. 10% DMSO (dimethyl sulfoxide). 0.1% Triton-X 100. 10 mM Tris [tris-(hydroxymethyl) aminomethane]acetic acid with a pH value of 5.0.

Formation of capsomeres can be monitored by electron microscopy, and, in instances wherein capsomeres are comprised of fusion proteins, the presence of various protein components in the assembled capsomere can be confirmed by Western blot analysis using specific antisera.

According to the present invention, methods are provided for therapeutic treatment of individuals infected with HPV comprising the step of administering to a patient in need thereof an amount of a vaccine formulation of the invention effective to reduce the level of HPV infection. The invention also provide methods for prophylactic treatment of individuals susceptible to HPV infection comprising the step of administering to an individual susceptible to HPV infection an amount of a vaccine formulation of the invention effective to prevent HPV infection. While infected individuals can be easily identified using standard diagnostic techniques, susceptible individuals may be identified, for example, as those engaged in sexual relations with an infected individual. However, due to the high frequency of HPV infection, all sexually active persons are susceptible to papilloma virus infection.

Administration of a vaccine formulation can include one or more additional components such as pharmaceutically acceptable carriers, diluents, adjuvants, and/or buffers. Vaccines may be administered at a single time or at multiple times. Vaccine formulation of the invention may be delivered by various routes including, for example, oral, intravenous, intramuscular, nasal, rectal, transdermal, vaginal, subcutaneous, and intraperitoneal administration.

Vaccine formulations of the invention offer numerous advantages when compared to conventional vaccine preparations. As part of a therapeutic vaccination, capsomeres can promote elimination of persistently infected cells in, for example, patients with CIN or cervical carcinoma. Additionally, therapeutic vaccinations of this type can also serve a prophylactic purpose in protecting patients with CIN lesions from re-infection. As an additional advantage, capsomeres can escape neutralization by pre-existing anticapsid antibodies and thereby posses longer circulating half-life as compared to chimeric virus-like particles.

Vaccine formulations comprising chimeric capsomeres can provide the additional advantage of increased antigenicity of both protein components of the fusion protein from which the capsomere is formed. For example, in a VLP, protein components of the underlying capsomere may be buried in the overall structure as a result of internalized positioning within the VLP itself. Similarly, epitopes of the protein components may be sterically obstructed as a result of capsomere-to-capsomere contact, and therefore unaccessible for eliciting an immune response. Preliminary results using L1/E7 fusion proteins to produce VLPs support this position in that no antibody response was detected against the E7 component. This observation is consistent with previous results which indicate that the carboxy terminal region of L1 forms inter-pentameric arm structures that allow assembly of capsomeres into capsids [Garcia, et al., J. Virol. 71: 2988–2995 (1997)]. Presumably in a chimeric capsomere structure, both protein components of the fusion protein substructure are accessible to evoke an immune response. Capsomere vaccines would therefore offer the additional advantage of increased antigenicity against any protein component, including, for example, neutralizing epitopes from other virus proteins, expressed as a fusion with L1 amino acid sequences.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is illustrated by the following examples. Example 1 describes construction of expression vectors to produce fusion, or chimeric, viral proteins. Example 2 relates to generation of recombinant baculoviruses for expression of viral proteins. Example 3 addresses purification of capsomeres. Example 4 describes an immunization protocol for production of antisera and monoclonal antibodies. Example 5 provides a peptide ELISA to quantitate capsomere formation. Example 6 describes an antigen capture ELISA to quantitate capsomere formation. Example 7 provides a hemagglutinin assay to assay for the induction of neutralizing antibodies.

EXAMPLE 1 Construction of Chimeric L1 Genes

DNA encoding the HPV 16 L1 open reading frame was excised from plasmid 16-114/k-L1/L2-pSynxtVI⁻ [Kirnbauer er al., J. Virol. 67:6929–6936 (1994)] using BglII and the resulting fragment subcloned into pUC19 (New England Biolabs. Beverly, Mass.) previously linearized at the unique BamHI restriction site. Two basic expression constructs were first generated to permit subsequent insertion of DNA to allow fusion protein expression. One construct encoded HPV 16 L1Δ310 having a nine amino acid deletion; the deleted region was known to show low level homology with all other papilloma virus L1 proteins. The second construct, HPV 16 L1 ΔC, encoded a protein having a 34 amino acid deletion of the carboxy terminal L1 residues. Other constructs include an EcoRV restriction site at the position of the deletion for facilitated insertion of DNA encoding other protein sequences. Addition of the EcoRV site encodes two non-L1 protein amino acids, aspartate and isoleucine.

A. Generation of an HPV 16 L1Δ310 Expression Construct

Two primers (SEQ ID NOs: 5 and 6) were designed to amplify the pUC19 vector and the complete HPV 16 L1 coding sequence, except nucleotides 916 through 942 in SEQ ID NO: 1. Primers were synthesized to also introduce a unique EcoRV restriction site (underlined in SEQ ID NOs: 5 and 6) at the termini of the amplification product.

CCCCGATATCGCCTTTAATGTATAAATCGTCTGG SEQ ID NO: 5 CCCCGATATCTCAAATTATTTTCCTACACCTAGTG SEQ ID NO: 6 The resulting PCR product was digested with EcoRV to provide complementary ends and the digestion product circularized by ligation. Ligated DNA was transformed into E. coli using standard techniques and plasmids from resulting colonies were screened for the presence of an EcoRV restriction site. One clone designated HPV 16 L1 Δ310 was identified as having the appropriate twenty-seven nucleotide deletion and this construct was used to insert DNA fragments encoding other HPV 16 proteins at the EcoRV site as discussed below. B. Generation of an HPV 16 L1 ΔC Expression Constructs

Two primers (SEQ ID NOs: 7 and 8) were designed complementary to the HPV 16 L1 open reading frame such that the primers abutted each other to permit amplification in reverse directions on the template DNA comprising HPV 16 L1-encoding sequences in pUC19 described above.

SEQ ID NO: 7 AAAGATATCTTGTAGTAAAAATTTGCGTCCTAAAGGAAAC SEQ ID NO: 8 AAAGATATCTAATCTACCTCTACAACTGCTAAACGCAAAAAACG Each primer introduced an EcoRV restriction site at the terminus of the amplification product. In the downstream primer (SEQ ID NO: 8), the EcoRV site was followed by a TAA translational stop codon positioned such that the amplification product, upon ligation of the EcoRV ends to circularize, would include deletion of the 34 carboxy terminal L1 amino acids. PCR was performed to amplify the partial L1 open reading frame and the complete vector. The amplification product was cleaved with EcoRV, circularized with T4 DNA ligase, and transformed into E. coli DH5 α cells. Plasmids from viable clones were analyzed for the presence of an EcoRV site which would linearize the plasmid. One positive construct designated pUCHPV16L1ΔC was identified and used to insert DNA from other HPV 16 proteins utilizing the EcoRV site. C. Insertion of DNA Fragments into HPV 16 L1 Δ310 and HPV16L1ΔC

DNA fragments of HPV 16 E7 encoding amino acids 1–50, 1–60, 1–98, 25–75, 40–98, 50–98 in SEQ ID NO: 4 were amplified using primers that introduced terminal 5′ EcoRV restriction sites in order to facilitate insertion of the fragment into either HPV 16 L1 Δ310 and HPV16L1ΔC modified sequence. In the various amplification reactions, primer E7.1 (SEQ ID NO: 9) was used in combination with primer E7.2 (SEQ ID NO: 10) to generate a DNA fragment encoding E7 amino acids 1–50: with primer E7.3 (SEQ ID NO: 11) generate a DNA fragment encoding E7 amino acids 1–60: or with primer E7.4 (SEQ ID NO: 12) generate a DNA fragment encoding E7 amino acids 1–98. In other amplification reactions, primer pairs E7.5 (SEQ ID NO: 13) and E7.6 (SEQ ID NO: 14) were used to amplify a DNA fragment encoding E7 amino acids 25–75: E7.7 (SEQ ID NO: 15) and E7.4 (SEQ ID NO: 12) were used to amplify a DNA fragment encoding E7 amino acids 40–98; and E7.8 (SEQ ID NO: 16) and E7.4 (SEQ ID NO: 12) were used to amplify a DNA fragment encoding E7 amino acids 50–98.

Primer E7.1 SEQ ID NO: 9 AAAAGATATCATGCATGGAGATACACCTACATTGC Primer E7.2 SEQ ID NO: 10 TTTTGATATCGGCTCTGTCCGGTTCTGCTTGTCC Primer E7.3 SEQ ID NO: 11 TTTTGATATCCTTGCAACAAAAGGTTACAATATTGTAATGGGCC Primer E7.4 SEQ ID NO: 12 AAAAGATATCTGGTTTCTGAGAACAGATGGGGCAC Primer E7.5 SEQ ID NO: 13 TTTTGATATCGATTATGAGCAATTAAATGACAGCTCAG Primer E7.6 SEQ ID NO: 14 TTTTGATATCGTCTACGTGTGTGCTTTGTACGCAC Primer E7.7 SEQ ID NO: 15 TTTATCGATATCGGTCCAGCTGGACAAGCAGAACCGGAC Primer E7.8 SEQ ID NO: 16 TTTTGATATCGATGCCCATTACAATATTGTAACCTTTTG

Similarly, nucleotides from DNA encoding the influenza matrix protein (SEQ ID NO: 17) was amplified using the primer pair set out in SEQ ID NOs: 19 and 20. Both primers introduced an EcoRV restriction site in the amplification product.

SEQ ID NO: 19 TTTTGATATCGATATGGAATGGCTAAAGACAAGACCAATC SEQ ID NO: 20 TTTTGATATCGTTGTTTGGATCCCCATTCCCATTG

PCR products from each amplification reaction were cleaved with EcoRV and inserted into the EcoRV site of either the HPV 16 L1 Δ310 and HPV16L1ΔC sequences previously linearized with the same enzyme. In order to determine the orientation of inserts in plasmids encoding E7 amino acids 25–75 and 50–98 and plasmid including influenza matrix protein, ClaI digestion was employed, taking advantage of a restriction site overlapping the newly created EcoRV restriction site (GATATCGAT) and included in the upstream primer. For the three expression constructs including the initiating methionine of HPV16 E7, insert orientation was determined utilizing a NslI restriction site within the E7 coding region.

Once expression constructs having appropriate inserts were identified, the protein coding region for both L1 and inserted amino acids was excised as a unit using restriction enzymes XbaI and SmaI and the isolated DNA ligated into plasmid pVL1393 (Invitrogen) to generate recombinant baculoviruses.

D. Elimination of EcoRV Restriction Sites in Expression Constructs

The HPV 16 L1 ΔC sequence includes DNA from the EcoRV site that results in translation of amino acids not normally found in wild-type L1 polypeptides. Thus, a series of expression constructions was designed in which the artificial EcoRv site was eliminated. The L1 sequence for this series of expression constructs was designated HPV 16L1ΔC*.

To generate an expression construct containing the HPV 16L1ΔC* sequence, two PCR reactions were performed to amplify two overlapping fragments from the pUC-HPV16 L1 ΔC encoding E7 amino acids 1–50. The resulting DNA fragments overlapped at the position of the L1/E7 boundary but did not contain the two EcoRV restriction sites. Fragment 1 was generated using primers P1 (SEQ ID NO: 21) and P2 (SEQ ID NO: 22) and fragment 2 using primers P3 (SEQ ID NO: 23) and P4 (SEQ ID NO: 24).

Primer P1 GTTATGACATACATACATTCTATG SEQ ID NO: 21 Primer P2 CCATGCATTCCTGCTTGTAGTAAAAATTTGCGTCC SEQ ID NO: 22 Primer P3 CTACAAGCAGGAATGCATGCAGATACACC SEQ ID NO: 23 Primer P4 CATCTGAAGCTTAGTAATGGGCTCTGTCCGGTTCTG SEQ ID NO: 24

Following the first two amplification reactions, the two purified products were used as templates in another PCR reaction using primers P1 and P4 only. The resulting amplification product was digested with enzymes EcoNI and HindIII inserted into the HPV 16L1 ΔC expression construct described above following digestion with the same enzymes. The resulting expression construct differed from the original HPV16L1 ΔC construct with DNA encoding L1 and E7 amino acids 1–50 by loss of the two internal EcoRV restriction sites. The first EcoRV site was replaced by DNA encoding native L1 alanine and glycine amino acids in this position and the second was replaced by a translational stop signal. In addition, the expression construct, designated HPV 16 L1 ΔC* E7 1–52, contained the first 52 amino acids of HPV 16 E7 as a result of using primer P4 which also encodes E7 amino acids residues histidine at position 51 and tyrosine at position 52. HPV 16 L1ΔC* E7 1–52 was then used to generate additional HPV 16 L1ΔC expression constructs further including DNA encoding E7 amino acids 1–55 using primer P1 (SEQ ID NO: 21) in combination with primer P5 (SEQ ID NO: 25), E7 amino acids 1–60 with primer pair P1 and P6 (SEQ ID NO: 26), and E7 amino acids 1–65 with primer pair P1 and P7 (SEQ ID NO: 27). The additional animo acid-encoding DNA sequences in the amplification products arose from design of the primers to include additional nucleotides for the desired amino acids.

Primer P5 SEQ ID NO: 25 CATCTGAAGCTTAACAATATTGTAATGGGCTCTGTCCG Primer P6 SEQ ID NO: 26 CATCTGAAGCTTACTTGCAACAAAAGGTTACAATATTGTAATGGGC TCTGTCCG Primer P7 SEQ ID NO: 27 CATCTGAAGCTTAAAGCGTAGAGTCACACTTGCAACAAAAGGTTAC AATATTGTAATGGGCTCTGTCCG Similarly. HPV 16 L1ΔC* E7 1–70 was generated using template DNA encoding HPV 16 L1ΔC* E7 1–66 and the primer pair P1 and P8 (SEQ ID NO: 28).

Primer P8 SEQ ID NO: 28 CATCTGAAGCTTATTGTACGCACAACCGAAGCGTAGAGTCACACTTG Following each PCR reaction, the amplification products were digested with EcoNI and HindIII and inserted into HPV16L1ΔC previously digested with the same enzymes. Sequences of each constructs were determined using an Applied Biosystems Prism 377 sequencing instrument with fluorescent chain terminating dideoxynucleotides [Prober et al., Science 238:336–341 (1987)].

EXAMPLE 2 Generation of Recombinant Baculoviruses

Spodoptera frugiperda (Sf9) cells were grown in suspension or monolayer cultures at 27° in TNMFH medium (Sigma) supplemented with 10% fetal calf serum and 2 mM glutamine. For HPV 16 L1-based recombinant baculovirus construction, Sf9 cells were transfected with 10 μg of transfer plasmid together with 2 μg of linearized Baculo-Gold DNA (PharMingen, San Diego, Calif.). Recombinant viruses were purified by according to manufacturer's suggested protocol.

To test for expression of HPV 16 L1 protein, 10⁵ Sf9 cells were infected with baculovirus recombinant at a multiplicity of infection (m.o.i) of 5 to 10. After incubation for three to four days at 28° C., media was removed and cells were washed with PBS. The cells were lysed in SDS sample buffer and analyzed by SDS-PAGE and Western blotting using, anti-HPV16 L1 and anti-HPV16 E7 antibodies.

In order to determine which of the chimeric L1 protein expression constructs would preferentially produce capsomeres, extracts from transfected cells were subjected to gradient centrifugation. Fractions obtained from the gradient were analyzed for L1 protein content by Western blotting and for VLP formation by electron microscopy. The results are shown in Table 1.

The intact HPV L1 protein, as well as the expression products HPV 16 L1Δ310 and HPV 16 L1ΔC. each were shown to produce capsomeres and virus-like particles in equal proportions. When E7 coding sequences were inserted into the HPV 16 L1Δ310 vector, only fusion proteins including E7 amino acids 1 to 50 produced gave rise to detectable capsomere formation.

When E7 encoding DNA was inserted into the HPV 16 L1ΔC vector, all fusion proteins were found to produce capsomeres; chimeric proteins including E7 amino acid residues 40–98 produced the highest level of exclusively capsomere structures. Chimeric proteins including E7 amino acids 1–98 and 25–75 both produced predominantly capsomeres, even thorough virus-like particle formation was also observed. The chimeric protein including E7 amino acids 1–60 resulted in nearly equal levels of capsomere and virus-like particle production.

When E7 sequences were inserted into the HPV 16 L1Δ*C vector, all fusion proteins were shown to produce capsomeres. Insertion of DNA encoding E7 residues 1–52, 1–55, and 1–60 produced the highest level of capsomeres, but equal levels of virus-like particle production were observed. While insertion of DNA encoding E7 DNA for residues 1–65, 1–70, 25–75, 40–98, and 1–98 resulted in comparatively lower levels or undetectable levels of capsid, capsomeres were produced in high quantities.

TABLE 1 Capsomeree and Capsid Forming Capacity of Chimeric HPV L1 Proteins L1 Expression Capsomere Capsid Construct Insert Yield Yield HPV 16 L1 None + + + + + + + + + + HPV 16 L1

310 None + + + + + HPV 16 L1

C None + + + + + + + + HPV 16 L1

310 E7 1–98 − − HPV 16 L1

310 E7 1–50 + + − HPV 16 L1

310 E7 25–75 − − HPV 16 L1

310 E7 50–98 − − HPV 16 L1

C E7 1–98 + + + + HPV 16 L1

C E7 25–75 + + + + HPV 16 L1

C E7 50–98 + + HPV 16 L1

C E7 1–60 + + + + + + + + + + HPV 16 L1

C E7 40–98 + + + + − HPV 16 L1

C Influenza + + + + HPV 16 L1

*C E7 1–52 + + + + + + + + + + HPV 16 L1

*C E7 1–55 + + + + + + + + + + HPV 16 L1

*C E7 1–60 + + + + + + + HPV 16 L1

*C E7 1–65 + + − HPV 16 L1

*C E7 1–70 + + −

EXAMPLE 3 Purification of Capsomeres

Trichopulsia ni (TN) High Five cells were grown to a density of approximately 2×10⁶ cells/ml in Ex-Cell 405 serum-free medium (JRH Biosciences). Approximately 2×10⁸ cells were pelleted by centrifugation at 1000×g for 15 minutes, resuspended in 20 ml of medium, and infected with recombinant baculoviruses at m.o.i of 2 to 5 for 1 hour at room temperature. After addition of 200 ml medium, cells were plated and incubated for 3 to 4 days at 27° C. Following incubation, cells were harvested, pelleted, and resuspended in 10 ml of extraction buffer.

The following steps were performed at 4° C. Cells were sonicated for 45 seconds at 60 watts and the resulting cell lysate was centrifuged at 10,000 rpm in a Sorval SS34 rotor. The supernatant was removed and retained while the resulting pellet was resuspended in 6 ml of extraction buffer, sonicated for an additional 3 seconds at 60 watts, and centrifuged again. The two supernatants were combined, layered onto a two-step gradient containing 14 ml of 40% sucrose on top of 8 ml of CsCl solution (4.6 g CsCl per 8 ml in extraction buffer), and centrifuged in a Sorval AH629 swinging bucket rotor for 2 hours at 27.000 rpm at 10° C. The interface region between the CsCl and the sucrose along with the CsCl complete layer were collected into 13.4 ml Quickseal tubes (Beckman) and extraction buffer added to adjust the volume 13.4 ml. Samples were centrifuged overnight at 50.000 rpm at 20° C. in a Beckman 70 TI rotor. Gradients were fractionated (1 ml per fraction) by puncturing tubes on top and bottom with a 21-gauge needle. Fractions were collected from each tube and 2.5 μl of each fraction were analyzed by a 10% SDS-polyacrylamide gel and Western blotting using an anti-HPV16 L1 antibody.

Virus-like particles and capsomeres were separated from the fractions identified above by sedimentation on 10 to 50% sucrose gradients. Peak fractions from CsCl gradients were pooled and dialyzed for 2 hours against 5 mM HEPES (pH 7.5). Half of the dialysate was used to produce capsomeres by disassembly of intact VLPs overnight by adding EDTA (final concentration 50 mM), EGTA (50 mM), DTT (30 mM). NaCl (100 mM), and Tris/HCl, pH 8.0, (10 mM). As control, NaCl and Tris/HCl only were added to the other half.

For analysis of capsomeres produced from disassembled VLPs, EDTA, EGTA and DTT (final concentration 5 mM each) were added to the sucrose cushions which were centrifuged at 250,000×g for 2 to 4 hours at 4° C. Fractions were collected by puncturing tubes from the bottom. A 1:10 dilution of each fraction was then analyzed by antigen capture ELISA.

EXAMPLE 4 Immunization Protocol for Production of Polyclonal Antisera and Monoclonal Antibodies

Balb/c mice are immunized subcutaneously three times, every four weeks with approximately 60 μg of HPV chimeric capsomeres mixed 1:1 with complete or incomplete Freund's Adjuvants in a total volume of 100 μl. Six weeks after the third immunization, mice are sacrificed and blood is collected by cardiac puncture.

EXAMPLE 5 Peptide ELISA to Quantitate Capsomere Formation

Microtiter plates (Dynatech) are coated overnight with 50 μl of peptide E701 [Muller et al., 1982] at a concentration of 10 μg/ml in PBS. Wells are blocked for 2 hour at 37° C. with 100 μl of buffer containing 5% BSA and 0.05% Tween 20 in PBS and washed three times with PBS containing 0.05% Tween 20. After the third wash. 50 μl of sera diluted 1:5000 in BSA/Tween 20/PBS is added to each well and incubation carried out for 1 hour. Plates are washed again as before and 50 μl of goat-anti-mouse peroxidase conjugate is added at a 1:5000 dilution. After 1 hour, plates are washed and stained using ABTS substrate (0.2 mg/ml. 2.2′-Azino-bis(3-ethylbenzhiazoline-β-sulfonic acid in 0.1 M Na-Acetate-Phosphate buffer (pH 4.2) with 4 μl 30% H₂O₂ per 10 ml). Extinction is measured after 1 hour at 490 nm in a Dynatech automated plate reader.

EXAMPLE 6 Antigen Capture ELISA to Quantitate Capsomere Formation

To allow relative quantification of virus-like particles and capsomeres in fractions of CsCl gradients, an antigen capture ELISA was utilized. Microtiter plates were coated overnight with 50 μl/well of a 1:500 dilution (final concentration of 2 μg per ml, in PBS) with a protein A purified mouse monoclonal antibody immunospecific for HPV 16 L1 (antibodies 25/C, MM07 and Ritti 1 were obtained from mice immunized with HPV 16 VLPs). Plates were blocked with 5% milk/PBS for 1 hour and 50 μl of fractions of CsCl gradients were added for 1 hour at 37° C. using a 1:300 dilution (in 5% milk/PBS). After three washings with PBS/0.05% Tween 20, 50 μl of a polyclonal rabbit antiserum (1:3000 dilution in milk/PBS), raised against HPV 16 VLPs was added and plates were incubated at 37° for 1 hour. Plates were washed again and further incubated with 50 μl of a goat-anti-rabbit peroxidase conjugate (Sigma) diluted 1:5000 in PBS containing 5% milk for 1 hour. After final washing, plates were stained with ABTS substrate for 30 minutes and extinction measured at 490 nm in a Dynatech automated plate reader. As a negative control, the assay also included wells coated only with PBS.

To test monoclonal antibodies for capsomere specificity, VLPs with EDTA/DTT to disassemble particles. Treated particle preparations were assayed in the antigen-capture ELISA and readings compared to untreated controls. For disassembly. 40 μl of VLPs was incubated overnight at 4° C. in 500 μl of disruption buffer containing 30 mM DTT. 50 mM EGTA, 60 mM EDTA, 100 mM NaCl, and 100 mM Tris/HCl, pH 8.0. Aliquots of treated and untreated particles were used in the above capture ELISA in a 1:20–1:40 dilution.

EXAMPLE 7 Hemagglutinin Inhibition Assay

In order to determine the extent to which chimeric capsomere vaccines evoke production of neutralizing antibodies, a hemagglutination inhibition assay is carried out as briefly described below. This assay is based on previous observations that virus-like particles are capable of hemagglutinizing red blood cells.

Mice are immunized with any of a chimeric capsomere vaccine and sera is collected as described above in Example 4. As positive controls, HPV16 L1 virus like particles (VLPs) and bovine PV1 (BPV) L1 VLPs are assayed in parallel with a chimeric capsomere preparation. To establish a positive baseline, the HPV16 or BPV1 VLPs are first incubated with or without sera collected from immunized mice after which red blood cells are added. The extent to which preincubation with mouse cera inhibits red blood cell hemagglutinization is an indication of the neutralizing capacity of the mouse sera. The experiments are then repeated using chimeric capsomeres in order to determine the neutralizing effect of the mouse sera on the vaccine. A brief protocol for the hemagglutination inhibition assay is described below.

One hundred microliters of heparin (1000 usp units/ml) are added to 1 ml fresh mouse blood. Red blood cells are washed three times with PBS followed by centrifugation and resuspension in a volume of 10 ml. Next, erythrocytes are resuspended in 0.5 ml PBS and stored at 4° C. for up to three days. For the hemagglutinin assay. 70 μl of the suspension is used per well on a 96-well plate.

Chimeric capsomere aliquots from CsCl gradients are dialyzed for one hour against 10 mM Hepes (pH 7.5) and 100 μl of two-fold serial dilutions in PBS are added to mouse erythrocytes in round-bottom 96-well microtiter plates which are further incubated for 3–16 hours at 4° C. For hemagglutination inhibition, capsomeres are incubated with dilutions of antibodies in PBS for 60 minutes at room temperature and then added to the erythrocytes. The level of erythrocyte hemagglutination, and therefore the presence of neutralizing antibodies, is determined by standard methods.

In preliminary results, mouse sera generated against chimeric capsomeres comprising HPV 16L1ΔC protein in association with E7 amino acid residues 1–98 was observed to inhibit hemagglutination by HPV16 VLPs, but not by BPV VLPs. The mouse sera was therefore positive for neutralizing antibodies against the human VLPs and this differential neutralization was most likely the result of antibody specificity for epitopes against which the antibodies were raised.

Numerous modifications and variations in the invention as set forth in the above illustrative examples are expected to occur to those skilled in the art. Consequently only such limitations as appear in the appended claims should be placed on the invention. 

1. A protein encoded by a nucleic acid molecule encoding a truncated HPV L1 protein, wherein said truncated HPV L1 protein is a protein of SEQ ID NO: 2 except that it is lacking one or more amino acids from its carboxy terminus, amino terminus or internal region and comprises only amino acids present in naturally occurring HPV proteins, and wherein said protein is immunogenic against HPV.
 2. A protein encoded by a nucleic acid molecule encoding a fusion protein, said fusion protein comprising an amino acid sequence of a truncated first HPV L1 protein and an amino acid sequence of a second HPV protein, wherein said first HPV L1 protein is a protein of SEQ ID NO: 2 except that it is lacking one or more amino acids from its carboxy terminus, amino terminus or internal region, said second HPV protein is selected from the group consisting of E1, E2, E3, E4, E5, E6 and E7, and said fusion protein comprises only amino acids present in naturally occurring HPV proteins, and wherein said fusion protein is immunogenic against HPV.
 3. A capsomere comprising a protein of claim
 1. 4. A capsomere comprising a protein of claim
 2. 5. A protein of claim 2, wherein said second HPV protein is an HPV E7 protein.
 6. A protein of claim 5, wherein said HPV E7 protein comprises amino acids 1–52 of an HPV E7 protein.
 7. A protein of claim 6, wherein said HPV E7 protein comprises amino acids 1–52 of SEQ ID NO:
 4. 8. A protein of claim 5, wherein said HPV E7 protein comprises amino acids 1–55 of an HPV E7 protein.
 9. A protein of claim 8, wherein said HPV E7 protein comprises amino acids 1–55 of SEQ ID NO:
 4. 10. A protein of claim 5, wherein said HPV E7 protein comprises amino acids 1–60 of an HPV E7 protein.
 11. A protein of claim 10, wherein said HPV E7 protein comprises amino acids 1–60 of SEQ ID NO:
 4. 12. A protein of claim 5, wherein said HPV E7 protein comprises amino acids 1–65 of an HPV E7 protein.
 13. A protein of claim 12, wherein said HPV E7 protein comprises amino acids 1–65 of SEQ ID NO:
 4. 14. A protein of claim 5, wherein said HPV E7 protein comprises amino acids 1–70 of an HPV E7 protein.
 15. A protein of claim 14, wherein said HPV E7 protein comprises amino acids 1–70 of SEQ ID NO:
 4. 